Step-by-step explanation:
1. (We) are studying our lessons in the library
2. (He) is my brother
3. Mr. Johnson is (my) favourite teacher
4. It was (them) who saves the girl from drowning
5.( I) am playing with my friends
6. The robber was caught by (him) and brought to the police station.
7. We are ready for (our) group project.
8.(I )want to talk to your parents.
9.(They) are planning a birthday party for me.
10.(It) is wonderful night.
Hope this helps you
have a good day :)